The different fatty acids composition of lecithins in the sarcoplasmic reticulum vesicles and the membranes of adrenal chromaffin granules.

Calcium transporting membranes of sarcoplasmic reticulum (SR) and amine transporting membranes of chromaffin granules (AG) isolated from different animal species (ox, rabbit and rat) show similar values for their phospholipid phases (0.5 mumole phospholipids/mg protein). The AG-membranes, however, contain higher lysolecithin (LPC) (10 11%) than the SR-membranes (2-6%). In both types of membrane a characteristic distribution of fatty acids was found in the phosphatidylcholine (PC) fraction. In SR-membranes 18-carbon fatty acids are present in increasing order of unsaturation (18:0 less than 18:1 less than 18:2) and in AG-membranes in decreasing order (18:0 greater than 18:1 greater than 18:2). The fatty acid composition of PCs specific of each membrane seems to be dependent on the presence of different endogenous lysolecithins and suggest a fatty acid turnover in both positions of the PC by the de- and re-acylation cycle. The importance in membranes function with regard to the Ca2+ transport of SR and the amine transport of AG membranes as related to the typical lipid phase is discussed.